1. Field of the Invention
The invention relates in general to industrial automation systems, and in particular to automation systems which comprise at least one bus system with bus subscribers connected to it and a central control device, and to a method for its operation.
2. Description of the Related Art
Control and Data Transmission Systems nowadays assume a leading position in industrial manufacture and system control owing to the high degree of automation that they make possible. The use of field bus systems is very widespread, via which a large number of decentralized input and output units are connected to a central control device.
However, there is an increasing desire and requirement to change the configuration of the bus system during a running process by connecting or disconnecting decentralized units, for example in order to make it possible to carry out a tool change on robots or to allow mobile units, which are planned to be connected to the bus only at times, to be included in the bus system and to be removed again or else to make it possible to carry out disconnection operations for only a limited time in a simple manner for maintenance purposes. Furthermore, interference, for example as a result of electromagnetic radiation, may be a reason for configuration changes to the bus system.
From networks such as the Ethernet, it is known that these networks continue processing in the event of changes to the configuration of connected appliances and ignore the subscriber that has been disconnected or has failed.
In order to comply with safety standards, field bus systems are, however, predominantly used in conjunction with safety-compliant bus components in automation engineering. In the case of INTERBUS systems, by way of example, it is possible to disconnect assemblies from the bus by means of appropriate switching commands for configuration changes. In this situation, as in the case of interference as well, the field bus system is reinitialized. This results in a brief interruption in data communication when configuration changes are made in these systems.
When the communication to a bus component is interrupted, it can thus maintain an emergency functionality provided that no hazardous process is controlled by this bus component. If hazardous processes are being controlled, safety can generally be ensured only by shutting down the machine that is being controlled. For this purpose, safety-compliant bus components frequently have an internal watchdog circuit arrangement, which is reset only after receiving appropriate information. If this information is not received, the process is automatically switched to a safe state.
Frequent configuration changes, particularly in the case of systems which also have safety-compliant bus components, accordingly reduce their availability.
The invention is based on the object of increasing the availability of automation systems. It would be advantageous to carry this out while complying with safety requirements, such that the bus system may have both safety-compliant bus subscribers and non-safety-compliant bus subscribers.